fix behavior of loops with external stream results (should terminate)

crates/nu-engine/src/compile/builder.rs

@@ -12,6 +12,7 @@ pub(crate) struct BlockBuilder {
     pub(crate) ast: Vec<Option<IrAstRef>>,
     pub(crate) register_allocation_state: Vec<bool>,
     pub(crate) file_count: u32,
+    pub(crate) loop_stack: Vec<LoopState>,
 }
 
 impl BlockBuilder {
@@ -24,6 +25,7 @@ impl BlockBuilder {
             ast: vec![],
             register_allocation_state: vec![true],
             file_count: 0,
+            loop_stack: vec![],
         }
     }
 
@@ -420,6 +422,69 @@ impl BlockBuilder {
         Ok(next)
     }
 
+    /// Push a new loop state onto the builder.
+    pub(crate) fn begin_loop(&mut self) {
+        self.loop_stack.push(LoopState::new());
+    }
+
+    /// True if we are currently in a loop.
+    pub(crate) fn is_in_loop(&self) -> bool {
+        !self.loop_stack.is_empty()
+    }
+
+    /// Add a loop breaking jump instruction.
+    pub(crate) fn push_break(&mut self, span: Span) -> Result<usize, CompileError> {
+        let index = self.jump_placeholder(span)?;
+        self.loop_stack
+            .last_mut()
+            .ok_or_else(|| CompileError::NotInALoop {
+                msg: "`break` called from outside of a loop".into(),
+                span: Some(span),
+            })?
+            .break_branches
+            .push(index);
+        Ok(index)
+    }
+
+    /// Add a loop continuing jump instruction.
+    pub(crate) fn push_continue(&mut self, span: Span) -> Result<usize, CompileError> {
+        let index = self.jump_placeholder(span)?;
+        self.loop_stack
+            .last_mut()
+            .ok_or_else(|| CompileError::NotInALoop {
+                msg: "`continue` called from outside of a loop".into(),
+                span: Some(span),
+            })?
+            .continue_branches
+            .push(index);
+        Ok(index)
+    }
+
+    /// Pop the loop state and set any `break` or `continue` instructions to their appropriate
+    /// target instruction indexes.
+    pub(crate) fn end_loop(
+        &mut self,
+        break_target_index: usize,
+        continue_target_index: usize,
+    ) -> Result<(), CompileError> {
+        let loop_state = self
+            .loop_stack
+            .pop()
+            .ok_or_else(|| CompileError::NotInALoop {
+                msg: "end_loop() called outside of a loop".into(),
+                span: None,
+            })?;
+
+        for break_index in loop_state.break_branches {
+            self.set_branch_target(break_index, break_target_index)?;
+        }
+        for continue_index in loop_state.continue_branches {
+            self.set_branch_target(continue_index, continue_target_index)?;
+        }
+
+        Ok(())
+    }
+
     /// Consume the builder and produce the final [`IrBlock`].
     pub(crate) fn finish(self) -> IrBlock {
         IrBlock {
@@ -436,3 +501,19 @@ impl BlockBuilder {
         }
     }
 }
+
+/// Keeps track of `break` and `continue` branches that need to be set up after a loop is compiled.
+#[derive(Debug)]
+pub(crate) struct LoopState {
+    break_branches: Vec<usize>,
+    continue_branches: Vec<usize>,
+}
+
+impl LoopState {
+    pub(crate) const fn new() -> Self {
+        LoopState {
+            break_branches: vec![],
+            continue_branches: vec![],
+        }
+    }
+}

crates/nu-engine/src/compile/call.rs

@@ -62,6 +62,12 @@ pub(crate) fn compile_call(
             "for" => {
                 return compile_for(working_set, builder, call, redirect_modes, io_reg);
             }
+            "break" => {
+                return compile_break(working_set, builder, call, redirect_modes, io_reg);
+            }
+            "continue" => {
+                return compile_continue(working_set, builder, call, redirect_modes, io_reg);
+            }
             "return" => {
                 return compile_return(working_set, builder, call, redirect_modes, io_reg);
             }

crates/nu-engine/src/compile/keyword.rs

@@ -539,9 +539,13 @@ pub(crate) fn compile_loop(
 ) -> Result<(), CompileError> {
     // Pseudocode:
     //
-    // LOOP: drain %io_reg
+    //       drop %io_reg
-    //       ...<block>...
+    // LOOP: ...<block>...
+    //       check-external-failed %failed_reg, %io_reg
+    //       drain %io_reg
+    //       branch-if %failed_reg, END
     //       jump %LOOP
+    // END:  drop %io_reg
     let invalid = || CompileError::InvalidKeywordCall {
         keyword: "loop".into(),
         span: call.head,
@@ -551,7 +555,10 @@ pub(crate) fn compile_loop(
     let block_id = block_arg.as_block().ok_or_else(invalid)?;
     let block = working_set.get_block(block_id);
 
-    let loop_index = builder.drain(io_reg, call.head)?;
+    builder.begin_loop();
+    builder.load_empty(io_reg)?;
+
+    let loop_index = builder.next_instruction_index();
 
     compile_block(
         working_set,
@@ -562,8 +569,27 @@ pub(crate) fn compile_loop(
         io_reg,
     )?;
 
+    // Check for failed externals, and drain the output
+    let failed_reg = builder.next_register()?;
+    builder.push(
+        Instruction::CheckExternalFailed {
+            dst: failed_reg,
+            src: io_reg,
+        }
+        .into_spanned(call.head),
+    )?;
+    builder.drain(io_reg, call.head)?;
+    let failed_index = builder.branch_if_placeholder(failed_reg, call.head)?;
+
     builder.jump(loop_index, call.head)?;
 
+    let end_index = builder.next_instruction_index();
+    builder.set_branch_target(failed_index, end_index)?;
+    builder.end_loop(end_index, loop_index)?;
+
+    // State of %io_reg is not necessarily well defined here due to control flow, so make sure it's
+    // empty.
+    builder.mark_register(io_reg)?;
     builder.load_empty(io_reg)?;
 
     Ok(())
@@ -579,13 +605,16 @@ pub(crate) fn compile_while(
 ) -> Result<(), CompileError> {
     // Pseudocode:
     //
-    // LOOP:  drain %io_reg
+    //        drop %io_reg
-    //        %io_reg <- <condition>
+    // LOOP:  %io_reg <- <condition>
     //        branch-if %io_reg, TRUE
     //        jump FALSE
     // TRUE:  ...<block>...
+    //        check-external-failed %failed_reg, %io_reg
+    //        drain %io_reg
+    //        branch-if %failed_reg, FALSE
     //        jump LOOP
-    // FALSE:
+    // FALSE: drop %io_reg
     let invalid = || CompileError::InvalidKeywordCall {
         keyword: "while".into(),
         span: call.head,
@@ -596,7 +625,10 @@ pub(crate) fn compile_while(
     let block_id = block_arg.as_block().ok_or_else(invalid)?;
     let block = working_set.get_block(block_id);
 
-    let loop_index = builder.drain(io_reg, call.head)?;
+    builder.begin_loop();
+    builder.load_empty(io_reg)?;
+
+    let loop_index = builder.next_instruction_index();
 
     compile_expression(
         working_set,
@@ -621,10 +653,29 @@ pub(crate) fn compile_while(
         io_reg,
     )?;
 
+    // We have to check the result for a failed external, and drain the output on each iteration
+    let failed_reg = builder.next_register()?;
+    builder.push(
+        Instruction::CheckExternalFailed {
+            dst: failed_reg,
+            src: io_reg,
+        }
+        .into_spanned(call.head),
+    )?;
+    builder.drain(io_reg, call.head)?;
+    let failed_index = builder.branch_if_placeholder(failed_reg, call.head)?;
+
     builder.jump(loop_index, call.head)?;
 
-    builder.set_branch_target(jump_false_index, builder.next_instruction_index())?;
+    let end_index = builder.next_instruction_index();
+    builder.set_branch_target(jump_false_index, end_index)?;
+    builder.set_branch_target(failed_index, end_index)?;
 
+    builder.end_loop(end_index, loop_index)?;
+
+    // State of %io_reg is not necessarily well defined here due to control flow, so make sure it's
+    // empty.
+    builder.mark_register(io_reg)?;
     builder.load_empty(io_reg)?;
 
     Ok(())
@@ -644,9 +695,11 @@ pub(crate) fn compile_for(
     // LOOP: iterate %io_reg, %stream_reg, END
     //       store-variable $var, %io_reg
     //       %io_reg <- <...block...>
+    //       check-external-failed %failed_reg, %io_reg
     //       drain %io_reg
+    //       branch-if %failed_reg, END
     //       jump LOOP
-    // END:
+    // END:  drop %io_reg
     let invalid = || CompileError::InvalidKeywordCall {
         keyword: "for".into(),
         span: call.head,
@@ -670,6 +723,9 @@ pub(crate) fn compile_for(
     // Ensure io_reg is marked so we don't use it
     builder.mark_register(io_reg)?;
 
+    // Set up loop state
+    builder.begin_loop();
+
     let stream_reg = builder.next_register()?;
 
     compile_expression(
@@ -711,24 +767,90 @@ pub(crate) fn compile_for(
         io_reg,
     )?;
 
+    // Check for failed external
+    let failed_reg = builder.next_register()?;
+    builder.push(
+        Instruction::CheckExternalFailed {
+            dst: failed_reg,
+            src: io_reg,
+        }
+        .into_spanned(call.head),
+    )?;
+
     // Drain the output
     builder.drain(io_reg, call.head)?;
 
+    // End the loop if there was a failure
+    let failed_index = builder.branch_if_placeholder(failed_reg, call.head)?;
+
     // Loop back to iterate to get the next value
     builder.jump(iterate_index, call.head)?;
 
     // Update the iterate target to the end of the loop
-    let target_index = builder.next_instruction_index();
+    let end_index = builder.next_instruction_index();
-    builder.set_branch_target(iterate_index, target_index)?;
+    builder.set_branch_target(failed_index, end_index)?;
+    builder.set_branch_target(iterate_index, end_index)?;
+
+    // Handle break/continue
+    builder.end_loop(end_index, iterate_index)?;
 
     // We don't need stream_reg anymore, after the loop
-    // io_reg is guaranteed to be Empty due to the iterate instruction before
+    // io_reg may or may not be empty, so be sure it is
     builder.free_register(stream_reg)?;
+    builder.mark_register(io_reg)?;
     builder.load_empty(io_reg)?;
 
     Ok(())
 }
 
+/// Compile a call to `break`.
+pub(crate) fn compile_break(
+    _working_set: &StateWorkingSet,
+    builder: &mut BlockBuilder,
+    call: &Call,
+    _redirect_modes: RedirectModes,
+    io_reg: RegId,
+) -> Result<(), CompileError> {
+    if builder.is_in_loop() {
+        builder.load_empty(io_reg)?;
+        builder.push_break(call.head)?;
+    } else {
+        // Fall back to calling the command if we can't find the loop target statically
+        builder.push(
+            Instruction::Call {
+                decl_id: call.decl_id,
+                src_dst: io_reg,
+            }
+            .into_spanned(call.head),
+        )?;
+    }
+    Ok(())
+}
+
+/// Compile a call to `continue`.
+pub(crate) fn compile_continue(
+    _working_set: &StateWorkingSet,
+    builder: &mut BlockBuilder,
+    call: &Call,
+    _redirect_modes: RedirectModes,
+    io_reg: RegId,
+) -> Result<(), CompileError> {
+    if builder.is_in_loop() {
+        builder.load_empty(io_reg)?;
+        builder.push_continue(call.head)?;
+    } else {
+        // Fall back to calling the command if we can't find the loop target statically
+        builder.push(
+            Instruction::Call {
+                decl_id: call.decl_id,
+                src_dst: io_reg,
+            }
+            .into_spanned(call.head),
+        )?;
+    }
+    Ok(())
+}
+
 /// Compile a call to `return` as a `return` instruction.
 ///
 /// This is not strictly necessary, but it is more efficient.

crates/nu-protocol/src/errors/compile_error.rs

@@ -136,6 +136,7 @@ pub enum CompileError {
     },
 
     #[error("Missing required declaration: `{decl_name}`")]
+    #[diagnostic(code(nu::compile::missing_required_declaration))]
     MissingRequiredDeclaration {
         decl_name: String,
         #[label("`{decl_name}` must be in scope to compile this expression")]
@@ -143,9 +144,18 @@ pub enum CompileError {
     },
 
     #[error("Invalid literal")]
+    #[diagnostic(code(nu::compile::invalid_literal))]
     InvalidLiteral {
         msg: String,
         #[label("{msg}")]
         span: Span,
     },
+
+    #[error("{msg}")]
+    #[diagnostic(code(nu::compile::not_in_a_loop))]
+    NotInALoop {
+        msg: String,
+        #[label("can't be used outside of a loop")]
+        span: Option<Span>,
+    },
 }